JPS61289068A - Method for stabilizing N-vinylformamide - Google Patents

Abstract

PURPOSE:To prevent deterioration of N-vinylformamide during distilling and storing for stabilization thereof, by adding a small amount of thiourea to the N-vinylformamide. CONSTITUTION:Thioureas such as thiourea and ethylenethiourea in an amount of 10-10,000ppm, preferably 100-5,000ppm based on N-vinylformamide are added to the N-vinylformamide and the mixture is distilled under reduced pressure to obtain the N-vinylformamide. A homopolymer of N-vinylformamide and a copolymer thereof with such as acrylamide are useful as an excellent flocculant. N-vinylformamide is obtained by reacting acetaldehyde with formamide to form N-(alpha-hydroxyethyl)formamide, followed by methoxylation and further thermal decomposition.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for stabilizing N-vinylformamide. More specifically, the present invention relates to a method for stabilizing N-vinylformamide. It is about how to prevent it.

(Prior Art) Homopolymers of N-vinylformamide or copolymers thereof with acrylamide, etc. are known as flocculants with excellent performance. A method is known in which N-(α-hydroxyethyl)formamide obtained by reacting N-(α-hydroxyethyl)formamide with formamide is methoxylated and then thermally decomposed.

H CH3C)IO+H2NCHO+ CH3CHNHCf
(O In the case of this production method for N-vinylformamide, the N-vinylformamide obtained by thermal decomposition in the final step is recovered as a mixture with methanol, but this mixture also contains by-products generated during the reaction. Therefore, it is necessary to distill this mixture to remove all the methanol and to separate the contained by-products, but in this case, there is a tendency for some of the N-vinylformamide to deteriorate. Therefore, there was a drawback that the recovery rate of N-vinylformamide decreased.

On the other hand, even when recovered N-vinylformamide was stored for a long period of time, a portion of it tended to deteriorate, depending on the storage conditions.

(Problems to be Solved by the Invention) In view of the above circumstances, the present inventors have determined that N-
We have repeatedly investigated various methods for preventing the deterioration of vinylformamide.

(Means for solving the problem) As a result, even if compounds such as hydroquinone, phenothiazine, and phenylenediamine, which are conventionally used as stabilizers for vinyl compounds, are added, the effect is insufficient, and there is no satisfactory solution. However, it has been found that N-vinylformamide can be particularly stabilized only when a specific compound as described below is added, and the present invention has been achieved based on this knowledge.

That is, the present invention provides a method for stabilizing N-vinylformamide by causing the presence of thioureas in N-vinylformamide.

The present invention will be explained in detail below.

The N-vinylformamide that is the object of the stabilization method of the present invention may be obtained by any manufacturing method, but for example, N-(α-hydroxyethyl)formamide obtained by reacting acetaldehyde and formamide may be used. Examples include N-vinylformamide obtained by methoxylating and then thermally decomposing the same.

The thioureas used as stabilizers for N-vinylformamide in the present invention usually include thiourea, ethylenethiourea, dimethylthiourea, diethylthiourea, and diphenylthiourea, among which thiourea and ethylenethiourea are particularly preferred. The amount of these thioureas used is usually 1 to N-vinylformamide.
0 to 10,000 ppms preferably 100 to 5,00
0 ppm is sufficient, but if this amount is too small, the deterioration of N-vinylformamide cannot be sufficiently suppressed,
On the other hand, if the amount is too large, there is no change in the effect, which is not only uneconomical, but also, if it is added during storage, it is not preferable because it becomes a hindrance to the polymerization of N-vinylformamide itself.

(Function) In the present invention, as mentioned above, due to the presence of thioureas, N-
It can prevent deterioration of N-vinylformamide and stabilize it during distillation purification or storage of vinylformamide. For example, thioureas used for stabilization during distillation purification include It is desirable to have a higher boiling point than that of N-vinylformamide, usually N-vinylformamide. In addition, when thioureas are used for stabilization during storage, when thioureas are used in a polymerization reaction, the presence of thioureas may have an adverse effect on the polymerization reaction if the amount used is within the above range. There isn't.

(Example) Next, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to the following embodiments as long as they do not exceed the gist thereof.

Examples 1 to 4 and Comparative Example I Thioureas (stabilizers) shown in Table 1 were added to 1 rim of a mixture containing 70% N-vinylformamide, 26 ml of methanol, and 4 ml of other organic components, and 6 gourds were added. - was distilled under reduced pressure to first distill out methanol and then to distill off N-vinylformamide. The bottom temperature at this time is 80℃
The distillation time was 180 minutes.

After the completion of distillation, we determined the recovery rate of N-vinylformamide that was distilled and recovered, and the Harz weight that remained as a residue.
The results shown in Table 1 were obtained.

Table 1 (Note) Examples and ratios are abbreviations of Kinsame Example 1, the same applies hereinafter Examples 5 to 7 and Comparative Examples 2 to 7 N-vinylformamide, stabilizers of the present invention shown in Table 2 Alternatively, a compound conventionally known as a stabilizer for divinyl compounds was added, and this was heat-treated at a temperature of 130°C for 1 hour to perform a stabilization test of N-vinylformamide. When the ratio was determined, the results shown in Table 2 were obtained.

Table 2 (Effects of the Invention) According to the present invention, by adding a small amount of thioureas to N-vinylformamide, deterioration of N-vinylformamide can be prevented and stabilization can be achieved. Therefore, for example, if thioureas are added during distillation of N-vinylformamide, part of the N-vinylformamide will be prevented from polymerizing and turning into a tar-like substance, thereby preventing N-vinylformamide from polymerizing and becoming tar-like.
This is preferred because the recovery rate of vinylformamide does not decrease.

It is also stable for long-term storage.

Claims (3)

[Claims] (1) A method for stabilizing N-vinylformamide, which is characterized by the presence of a thiourea in N-vinylformamide. (2) The stabilization method according to claim (1), wherein the thiourea is thiourea or ethylenethiourea. (3) The stabilization method according to claim (1) or (2), wherein the amount of thioureas present is 10 to 10,000 ppm relative to N-vinylformamide.